spawn.py 文件源码

def _fixup_main_from_name(mod_name):
    # __main__.py files for packages, directories, zip archives, etc, run
    # their "main only" code unconditionally, so we don't even try to
    # populate anything in __main__, nor do we make any changes to
    # __main__ attributes
    current_main = sys.modules['__main__']
    if mod_name == "__main__" or mod_name.endswith(".__main__"):
        return

    # If this process was forked, __main__ may already be populated
    if getattr(current_main.__spec__, "name", None) == mod_name:
        return

    # Otherwise, __main__ may contain some non-main code where we need to
    # support unpickling it properly. We rerun it as __mp_main__ and make
    # the normal __main__ an alias to that
    old_main_modules.append(current_main)
    main_module = types.ModuleType("__mp_main__")
    main_content = runpy.run_module(mod_name,
                                    run_name="__mp_main__",
                                    alter_sys=True)
    main_module.__dict__.update(main_content)
    sys.modules['__main__'] = sys.modules['__mp_main__'] = main_module